Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens. The zoom lens is considered suitable for an image pickup apparatus using an image sensor, such as a digital still camera, a video camera, a monitoring camera, or a broadcasting camera, or an image pickup apparatus such as a camera using a silver-halide photographic film, for example.
Description of the Related Art
In recent years, image pickup apparatuses using a solid-state image sensor, such as a digital camera and video camera, have achieved high functionality and a decrease in size of the entire apparatus. Zoom lenses used in these apparatuses are required to be small and have high magnification and favorable optical performance. To respond to these demands, a zoom lens including a lens unit having positive, negative, and positive refractive power in order from an object side to an image side is known.
A zoom lens discussed in Japanese Patent Application Laid-Open No. 2013-190741 describes a zoom lens with high magnification exceeding 90 times, by moving a first lens unit to the object side in a large zooming range.
If an amount of movement of the first lens unit to an object side in zooming is made too large to realize high magnification in the zoom lens, the overall lens length is increased. This is particularly true in a zoom lens including lens units having positive, negative, and positive refractive power in order from the object side to an image side, as each lens unit needs to be accurately controlled during zooming. Therefore, for example, if the refractive power of a second lens unit serving as a magnification varying unit is excessively increased, excessive curvature of field is often generated.